The present invention generally relates to a method of manufacturing a semiconductor device and more particularly to methods of chemical/mechanical polishing of the surface of a semiconductor device.
The chemical/mechanical polishing (CMP) has been used for planarization of interlayer insulating films, metal interconnections, polysilicon filling device isolation trenches, etc.
In planarizing polysilicon by CMP, a stopper film consisting of silicon dioxide or nitride silicon is used in order to stop the progress of polishing after planarization. In this case, it is required to polish polysilicon selectively in comparison with the stopper film.
In the CMP, however, polishing/etching is performed based on the combined action of the chemical action of a polishing slurry and the mechanical action of abrasive grains. Depending on selected polishing conditions, therefore, “dishing” may occur. The “dishing” means that a recess 102 is formed, as shown in FIG. 1, on top of polysilicon 101 that fills a trench 100 after polishing. The occurrence of the “dishing” causes a degradation in the device performance, a reduction in the device yield, and a decrease in the device reliability.
In particular, the “dishing” remarkably occurs in wide trenches when trenches of different widths are simultaneously filled with polysilicon (at a rate more than twenty times that for narrow trenches). It is thought that the dishing occurs due to deformation of a polishing pad and a difference in polishing rate between polysilicon and stopper film. An improvement can be made through the use of a polishing pad of high elastic modulus and a fixed abrasive grain type of grinding stone.
However, since the polishing pad of high elastic modulus and the fixed abrasive grain type of grinding stone are stiff, it is known that a load is concentrated on a portion of abrasive grains at CMP time and consequently scratching becomes easy to occur on the polished surface of a semiconductor device. The “scratching” means that the polished surface 103 of the semiconductor device gets scratches 104 as shown in FIG. 2. As is the case with the “dishing”, the occurrence of the “scratching” causes a degradation in the device performance, a reduction in the device yield, and a decrease in the device reliability.
It is said that the stiff polishing pad is not suited for polishing semiconductor devices because it, while being capable of suppressing the dishing, makes the scratching easy to occur.